1. Field of the Invention
Embodiments of the present invention relate to an electromechanical transducer element, a droplet discharge head including the electromechanical transducer element, and a droplet discharge device including the droplet discharge head.
2. Description of the Related Art
A droplet discharge head is utilized as a recording head of an inkjet image forming device, such as a copier, a printer, a facsimile machine, and a plotter. Here, the image forming device forms an image on a recording material. The recording material is not limited to a paper. Namely, the image forming device forms an image by applying liquid droplets onto any recording material, such as a line, a fiber, a fabric, leather, a metal, a plastic, a glass, a timber, or a ceramic. Further, forming an image means not only to add an image having a meaning, such as a character or a graphic, to a recording media, but also to add an image having no meaning, such as a pattern, to a recording media (simply to apply liquid droplets to the medium). Further, a liquid discharged as the liquid droplets is not limited to “an ink,” and the liquid is not particularly limited, provided that the liquid is in a liquid phase at a time in which the liquid is discharged. Examples of the liquid include a DNA sample, a resist, and a pattern material.
As the droplet discharge head, the droplet discharge head having the following configuration has been known. Namely, the configuration includes a nozzle (discharge port) for discharging liquid droplets, a compression chamber that communicates with the nozzle, and a discharge driving unit for increasing the pressure of the liquid inside the compression chamber. In the droplet discharge head having such a configuration, the pressure of the liquid inside the compression chamber is increased by driving the discharge driving unit. The liquid droplets are discharged from the nozzle by forcing out the liquid blocking the nozzle and being in a meniscus state by the increased pressure. Several types of the discharge driving units have been known. For example, the following configuration has been known. Namely, in the configuration, a part of walls of a compression chamber is formed of an oscillation plate, and an electromechanical transducer element including an electromechanical transducer film disposed between electrodes is attached to the oscillation plate. The pressure of the liquid inside the compression chamber is increased through the oscillation plate, when a predetermined drive voltage is applied to the electromechanical transducer element, and thereby the electromechanical transducer element is deformed.
The electromechanical transducer film included in the electromechanical transducer element is formed of, for example, a complex oxide including lead, zirconia, and titanium (hereinafter, referred to as PZT), which is a ferroelectric substance having the perovskite structure. Such a ferroelectric substance having the perovskite structure has a morphotropic phase boundary (MPB). For example, in the case of Pb(ZrxTi1-xO3), the MPB exists in the vicinity of the content ratio of x=0.52 of Zr. When x is less then 0.52, the crystalline structure is tetragonal. On the other hand, when x is greater than 0.52, the crystalline structure is rhombohedral. In the electromechanical transducer film, the dielectric constant and the piezoelectric property become significantly larger in the vicinity of the MPB, and an excellent electromechanical transducing characteristic is obtained in the vicinity of the MPB. Therefore, the electromechanical transducer film is formed so that the content ratio of Zr is in the vicinity of the specific content ratio of Zr, which corresponds to the MPB.
As a method of producing an electromechanical transducer film formed of the PZT, the following method has been known. Namely, in the method, a PZT precursor film is formed by applying a PZT precursor solution onto an electrode using a chemical solution deposition method (CSD method), such as the sol-gel method and the MOD method, and the electromechanical transducer film of the PZT is obtained by baking and crystallizing the PZT precursor-coating film.
Patent Document 1 (Japanese Published Unexamined Application No. 2004-268414) discloses a method of laminating thin films of the PZT in which application and baking of the PZT precursor solution are repeated several times, until an electromechanical transducer film having a desired thickness is formed. In this manner, an electromechanical transducer film having a desired thickness is formed and a desired electromechanical transducing characteristic is obtained. At the same time, during the formation of the electromechanical transducer film, cracks can be prevented from occurring.
Patent Document 2 (Japanese Published Unexamined Application No. 2010-214800) discloses a method of producing an electromechanical transducer film. In the method, the following processes are repeated several times. Namely, the processes include a precursor film forming process of forming a PZT precursor film, an adjustment film forming process of forming an adjustment film that includes Ti and that adjusts composition of an electromechanical transducer film, and a baking process of collectively baking the precursor film and the adjustment film.
Patent Document 3 (Japanese Registered Patent No. 4283036) discloses a method of forming a film. In the method, a first solution and a second solution including the same types of solute components are utilized. Here, the first solution and the second solution are for forming a PZT film. In the method, the PZT film having a desired thickness is epitaxially formed on a substrate by alternately laminating a first coating film and a second coating film several times. Here, the first coating film is formed by applying the first solution, and the second coating film is formed by applying the second solution having a higher viscosity than that of the first solution. The titanium concentration in the first solution is higher than the titanium concentration in the second solution.